Reduced toxicity hypergolic propellants

ABSTRACT

The disclosure described herein is a reduced toxicity rocket propellant comprising a liquid fuel and a liquid oxidizer that ignites spontaneously upon contact with each other. The rocket propellant includes a metal hydride catalyst. Multiple embodiments of the propellant include multiple compositions of liquid fuel.

REFERENCE TO RELATED APPLICATIONS

The present application claims priority from U.S. Provisional Patent Application Ser. No. 61/480,595, filed on Apr. 29, 2011, entitled “REDUCED TOXICITY HYPERGOLIC PROPELLANTS”, the disclosure of which is expressly incorporated by reference.

FIELD

This disclosure pertains to the field of rocket propellants, in particular, hypergolic propellants.

BACKGROUND

In general, the use of hypergolic propellants is appropriate for a broad range of applications for both rocket and missile propulsion systems due to several key benefits including: 1) not needing an external ignition source which results in reduced weight, 2) reducing the number of needed parts in the system which typically increases reliability, and 3) the ability to generate small, repeated impulse bits for precise in-space maneuvers. To evaluate the performance of hypergolic propellants, there are three primary figures of merit. The first primary figure of merit is specific impulse, notated I_(sp), which is indicative of the energy content of the propellant; higher values are better. The second primary figure of merit is ignition delay which is defined as the time it takes for a propellant to form a combustion flame after initial contact of the liquid fuel and oxidizer; lower values are better. The third primary figure of merit is long term stability, since missions can often last many months or years in storage in a variety of ambient conditions. It is also desirable that the propellants also maintain its chemical and physical properties over time (i.e., it retains its hypergolicity and does not discolor, evaporate, or precipitate).

Current state-of-the-art hypergolic propellant combinations typically include hydrazine fuel or one of its derivatives such as monomethylhydrazine (MMH), unsymmetrical dimethylhydrazine (UDMH), or some mixture of the two, and liquid oxidizers typically include nitric acid and nitrogen tetroxide (NTO). As a major drawback, hydrazine and its derivatives are recognized as carcinogenic substances, nitric acid is extremely corrosive, and NTO and its derivatives are toxic and lethal upon acute exposure. Consequently, special precautions are needed in order to safely handle typical hypergolic propellants and involve expensive training, infrastructure, and disposal to manage the hazardous chemicals.

Various embodiments of the present invention provide new and nonobvious improvements in the field of hypergolic propellants.

SUMMARY

The disclosure includes a reduced toxicity hypergolic propellant comprising a liquid fuel and a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and the liquid fuel comprises kerosene, at least 20% triethylene glycol dimethyl ether (triglyme) by weight, and at least 1% metal hydride by weight. In some embodiments, the hydrogen peroxide is high test hydrogen peroxide. In certain embodiments, the liquid fuel includes an amount of kerosene within the range of 20% to 75% by weight. In certain embodiments, the liquid fuel includes an amount of triethylene glycol dimethyl ether within the range of 20% to 80% by weight. In some embodiments, the metal hydride is sodium borohydride. In further embodiments, the liquid fuel includes an amount of sodium borohydride within the range of 5% to 15% by weight. In certain embodiments, the liquid fuel includes a cobalt compound.

The disclosure also includes a reduced toxicity hypergolic propellant comprising a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising kerosene, sodium borohydride, and an amount of triethylene glycol dimethyl ether sufficient to dissolve the sodium borohydride.

The disclosure also includes a reduced toxicity hypergolic propellant comprising a liquid fuel and a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide, the liquid fuel comprising, by weight, approximately 33.3% kerosene, approximately 58.7% triethylene glycol dimethyl ether (triglyme), and approximately 8% sodium borohydride.

The disclosure further includes a reduced toxicity hypergolic propellant comprising a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising dimethylformamide and at least 1% metal hydride by weight. In some embodiments, the liquid fuel includes an amount of metal hydride within the range of 1% to 18% by weight. In some embodiments, the metal hydride is sodium borohydride. In further embodiments, the liquid fuel includes an amount of sodium borohydride within the range of 5% to 18% by weight, and an amount of dimethylformamide within the range of 82% to 95% by weight. In certain embodiments, the liquid fuel includes a cobalt compound.

The disclosure also includes a reduced toxicity hypergolic propellant comprising a liquid fuel and a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide, the liquid fuel comprising, by weight, approximately 88% dimethylformamide, and approximately 12% sodium borohydride.

The disclosure further includes a reduced toxicity hypergolic propellant comprising a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising dimethyl sulfoxide and at least 1% metal hydride by weight. In some embodiments, the liquid fuel includes an amount of metal hydride within the range of 1% to 15% by weight. In certain embodiments, the metal hydride is sodium borohydride. In further embodiments, the liquid fuel includes an amount of sodium borohydride within the range of 5% to 15% by weight and an amount of dimethyl sulfoxide within the range of 85% to 95% by weight. In some embodiments, the liquid fuel is approximately 10% sodium borohydride. In certain embodiments the liquid fuel includes a cobalt compound.

The disclosure also includes a reduced toxicity hypergolic propellant comprising a liquid fuel and a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide, the liquid fuel comprising, by weight, approximately 94.7% dimethyl sulfoxide, and approximately 5.3% sodium borohydride.

The disclosure further includes a reduced toxicity hypergolic propellant comprising a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising tetraethyl glycol and at least 1% metal hydride by weight. In certain embodiments, the metal hydride is sodium borohydride. In further embodiments, the liquid fuel includes an amount of sodium borohydride within the range of 5% to 15% by weight, and an amount of tetraethyl glycol within the range of 85% to 95% by weight. In some embodiments, the liquid fuel includes a cobalt compound.

The disclosure also includes a reduced toxicity hypergolic propellant comprising a liquid fuel and a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide, the liquid fuel comprising, by weight, approximately 87.7% tetraethyl glycol dimethyl ether (tetraglyme), and approximately 12.3% sodium borohydride.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned and other features of this disclosure, and the manner of attaining them, will become more apparent and the disclosure itself will be better understood by reference to the following description of embodiments of the disclosure taken in conjunction with the accompanying drawings, wherein:

FIG. 1A is an image of a prepared solution of dimethyl sulfoxide and sodium borohydride according to one embodiment of the present invention.

FIG. 1B is an image of a prepared solution of dimethylformamide and sodium borohydride according to one embodiment of the present invention.

FIG. 2 is a stacked image sequence illustrating a series of images of a drop test exhibiting successful ignition. Circles are superimposed to locate the oxidizer droplet.

FIG. 3 is a schematic of a rocket combustion chamber assembly used for evaluation of hypergolic propellants. SS indicates a part made from stainless steel and CS indicates a part made from carbon steel.

FIG. 4 is a stacked image sequence illustrating a series of images of an open chamber test exhibiting successful ignition.

FIG. 5 is a pressure trace chart of a nozzled-chamber test with the disclosed exemplary composition of Formulation B and 90.6% hydrogen peroxide.

FIG. 6 is an image of a coating of oxide powder on chamber hardware after testing the exemplary composition of Formulation B.

FIG. 7 is a pressure trace chart of a nozzled-chamber test with the disclosed exemplary composition of Formulation C and 90.6% hydrogen peroxide. Note the spike at approximately 3.15 seconds indicates slight overpressure.

FIG. 8 is an image of a coating of oxide powder, on chamber hardware after testing the exemplary embodiment of Formulation C.

FIG. 9 is a pressure trace chart of a nozzled-chamber test with the disclosed exemplary embodiment of Formulation D and 90.6% hydrogen peroxide.

FIG. 10 is an image of a coating of oxide powder on chamber hardware after testing the exemplary embodiment of Formulation D.

Although the drawings represent embodiments of the present disclosure, the drawings are not necessarily to scale and certain features may be exaggerated in order to better illustrate and explain the present disclosure.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. At least one embodiment of the present invention will be described and shown, and this application may show and/or describe other embodiments of the present invention. It is understood that any reference to “the invention” is a reference to an embodiment of a family of inventions, with no single embodiment including an apparatus, process, or composition that should be included in all embodiments, unless otherwise stated. Further, although there may be discussion with regards to “advantages” provided by some embodiments of the present invention, it is understood that yet other embodiments may not include those same advantages, or may include yet different advantages. Any advantages described herein are not to be construed as limiting to any of the claims.

Although various specific quantities (spatial dimensions, temperatures, pressures, times, force, resistance, current, voltage, concentrations, wavelengths, frequencies, heat transfer coefficients, dimensionless parameters, etc.) may be stated herein, such specific quantities are presented as examples only, and further, unless otherwise noted, are approximate values, and should be considered as if the word “about” prefaced each quantity. Further, with discussion pertaining to a specific composition of matter, that description is by example only, and does not limit the applicability of other species of that composition, nor does it limit the applicability of other compositions unrelated to the cited composition.

The invention described herein is an improvement over state-of-the-art MMH/NTO hypergolic propellants due to its reduced toxicity, significantly lower costs, and simplified handling requirements.

Theoretical Performance

Propellant development initially involved a trade study to determine its candidacy as viable hypergolic alternatives to MMH/NTO. Relying on a primary figure of merit, I_(sp), the theoretical value of a given propellant is estimated using a freely distributed thermochemistry code, Air Force I _(sp), with necessary chemical properties from appropriate Merck Index, National Institute of Standards and Technology (NIST), or Material Safety Data Sheet (MSDS) references. As a cutoff, I_(sp) values had to be greater than or equal to 290.0 seconds (85% relative performance compared to MMH/NTO). Furthermore, toxicology data from the MSDS's provided a means to evaluate whether the propellants would be safer and easier to handle.

General Composition and Preparation of Propellants

The disclosure described herein is a catalyzed liquid fuel that reacts hypergolically with a liquid oxidizer, such as hydrogen peroxide or rocket grade hydrogen peroxide. Hydrogen peroxide is a strong oxidizer capable of use as either a mono-component propellant or as an oxidizer component for multi-component propellants.

Hydrogen peroxide can vary in concentration from approximately 70% to approximately 100% weight with respect to water. High test hydrogen peroxide (also generally known as high strength hydrogen peroxide) is generally described as approximately 85% weight or greater hydrogen peroxide. High test hydrogen peroxide also includes up to approximately 98% weight concentration solution of hydrogen peroxide.

Catalyzed liquid fuel is generally described as a liquid solvent mixed with a metal hydride. The metal hydride is typically present in concentrations ranging from 0.1% to 25% on a weight-to-weight basis. In certain embodiments, the metal hydride is present in concentrations ranging from 1% to 18%, from 1% to 15%, from 5% to 18%, or from 5% to 15% on a weight-to-weight basis.

On a physical level, the hypergolic reaction is specifically initiated by the interaction between the peroxide and metal compound. Due to its inherent incompatibility, contact of these two components will rapidly initiate thermal decomposition of the peroxide to a maximum temperature of approximately 1300° F. During this decomposition process, the intermediate temperature will eventually reach the flash point of the solvent and results in a sustainable combustion flame. Ideally then, the catalyst is a compound that is rapidly oxidized by hydrogen peroxide, and furthermore the solvent should have a low flash point (thus requiring less time to reach its combustion temperature).

The exemplary solvents are polar, aprotic chemicals such as, but not limited to, dimethylformamide, dimethyl sulfoxide, triethylene glycol dimethyl ether (triglyme), and tetraethylene glycol (tetraglyme). The exemplary metal hydride is sodium borohydride due to its relatively low cost and its relatively lower reactivity when exposed to ambient moisture; however water-contamination should be avoided by handling the metal hydride in an inert environment (i.e., a desiccated argon glovebox). Other metal hydrides that may be suitable for use in catalyzed liquid fuel include, but are not limited to, lithium borohydride, copper hydride, sodium hydride, aluminum-containing hydrides, such as lithium aluminum hydride, beryllium-containing hydrides, magnesium hydride, and zinc hydride. Lithium-containing hydrides and beryllium-containing hydrides are significantly more toxic than sodium-containing hydrides.

For a typical mixture, 0.1% to 25% by weight of metal hydride is added to a solvent that has been pre-heated to approximately 95° F. on a hotplate and stirred with a magnetic bar for approximately one hour until the metal hydride is visibly dissolved. As shown in FIGS. 1A and 1B, solutions are either translucent (FIG. 1A) or have a slightly cloudy appearance (FIG. 1B). The prepared solution is then stored in plastic or glass containers at room temperature or in a chilled freezer at −22° F. for temperature stability observations.

Kerosene is a mixture of hydrocarbon chains typically within the range of approximately six (6) to approximately fifteen (15) carbon atoms per molecule. Unlike the exemplary solvents discussed above, kerosene is nonpolar. Kerosene is also significantly less expensive than the exemplary solvents discussed above. Kerosene, specifically RP-1, is used as a non-hypergolic rocket fuel in combination with liquid oxygen. A combination of kerosene, a metal hydride, and a polar, aprotic chemical solvent provides a catalyzed liquid fuel with hypergolic properties.

For a typical mixture including kerosene, the liquid fuel may include 0.1% to 75% by weight of kerosene, 20% to 80% by weight of polar, aprotic chemical solvent, and 0.1% to 25% by weight of metal hydride. In certain embodiments, the liquid fuel may include 0.1% to 75% by weight of kerosene, 20% to 80% by weight of triglyme, and 5% to 15% by weight of sodium borohydride. In further embodiments, the liquid fuel may include 20% to 75% by weight of kerosene, 20% to 80% by weight of triglyme, and 5% to 15% by weight of sodium borohydride. In some embodiments, the liquid fuel may include sodium borohydride, kerosene, and an amount of triglyme sufficient to dissolve the sodium borohydride. In some embodiments, prepared liquid fuel including kerosene, triglyme, and sodium borohydride is stored in a low-light environment at approximately 60° F. to 70° F.

Propellant Screening and Performance Measurement Methods

To actually demonstrate the propellants' performance, three phases of experimental testing were carried out. The first test is commonly referred to as a drop test whereby approximately 0.5 mL of oxidizer is dropped into a container filled with approximately 10 mL of prepared fuel from a height of 2 inches for typically three or more trials. A high speed camera records the interaction between the liquid droplets at 2000 frames per second (temporal resolution of 0.5 ms) and the ignition delay is measured as the time between initial contact of the droplets and the presence of a flame front. Based on general rules for rocket combustion residence times, an ignition delay of 30 ms or less was determined to be adequate for drop testing, assuming that the increased mixing efficiency of a properly designed injector would approximately halve the measured delay time. FIG. 2 depicts a stacked image sequence of a drop test exhibiting successful ignition.

The second experimental test is to evaluate possible propellant degradation over time. Samples were stored at ambient conditions or in a freezer chilled to −22° F. in non-airtight glass vials for several months. Propellants would exhibit one of three behaviors:

-   -   1. The solvent would evaporate, leaving behind the metal hydride         solid.     -   2. The metal hydride would precipitate and collect on the bottom         of the vial. Agitation of the solution would redissolve the         metal hydride.     -   3. The propellant would maintain a clear, transparent appearance         indicating that the metal hydride remains fully dissolved.

The third experimental test is to measure ignition delay. An actual rocket combustion chamber assembly and supporting feed system was designed with emphasis on the injector to provide the best possible mixing. FIG. 3 depicts a schematic of the rocket combustion chamber assembly. To measure ignition delay, the fuel and oxidizer were pumped through the injectors in open air with video recorded by a high speed camera at 2000 frames per second. FIG. 4 depicts a stacked image sequence of a chamber test exhibiting successful ignition. Counting the frames between fuel/oxidizer contact and the appearance of a combustion flame would then give the ignition delay with an accuracy of +/−0.5 ms. If values were less than 15 ms (again based on general rules for rocket combustion residence times) the combustion chamber and nozzle would be installed, and the test would be repeated to measure the pressure transient at ignition and during steady-state operation in efforts to determine whether the propellant will inherently sustain a stable combustion flame.

Formulation A

In some embodiments, a liquid fuel comprises metal hydride, kerosene, and an amount of triethylene glycol dimethyl ether sufficient to dissolve the metal hydride. In certain embodiments, a liquid fuel comprises, by weight, at least 1% metal hydride, at least 20% kerosene, and at least 20% triethylene glycol dimethyl ether. In further embodiments, a liquid fuel comprises, by weight, 5% to 15% sodium borohydride, 20% to 75% kerosene, and 20% to 80% triethylene glycol dimethyl ether.

One exemplary composition comprises, by weight, 33.3% jet-A kerosene, 58.7% triethylene glycol dimethyl ether (also described as triglyme) and 8% sodium borohydride that creates a translucent, yellow solution with no visible precipitates. Formulation A presents a potential method of rendering many kerosene fuels (i.e., jet-A, jet-A-1, RP-1, JP-4, JP-8) hypergolic which is of importance due to kerosene's stability, ease of handling, and non-toxic properties. Thermochemistry indicates a vacuum theoretical I_(sp) of 314.01 seconds and a theoretical I_(sp) of 299.1 seconds with an optimal oxidizer-to-fuel (O/F) ratio of 5.54. The fuel did not recrystallize during a one month period of storage at ambient temperatures at about 65° F. and also did not recrystallize over a six month period when stored in a freezer at −20° F. Measurements from drop tests indicate an ignition delay of 21.0 ms with 85.6% peroxide. Chamber testing has yet to be completed for this formulation.

As a comparison to the liquid fuel of Formulation A, drop tests performed on liquid fuel compositions consisting of, by weight, 1%, 7%, and 11% sodium borohydride in triglyme (without kerosene) indicate ignition delays of (no ignition), 22.0 ms, and 24.3 ms, respectively, with 87.4% peroxide. Drop tests performed on a liquid fuel composition consisting of, by weight, 8% sodium borohydride in triglyme (without kerosene) indicate an average ignition delay of 6.2 ms with 98% peroxide and 10.6 ms with 88.5% hydrogen peroxide. Open-air testing with an injector assembly resulted in an ignition delay of 9.0 ms with 90.6% peroxide. Thermochemistry indicates a maximum theoretical I_(sp) of 336.7 seconds with an optimal oxidizer-to-fuel (O/F) ratio of 2.81.

MSDS indicates that breathing triglyme fumes or direct contact with skin may cause irritation; however there are no recognizable carcinogens or toxins. MSDS indicates that kerosene is harmful or fatal if swallowed, harmful by inhalation, and may irritate the eyes, respiratory system, and skin. Kerosene is not listed as carcinogenic by the National Toxicology Program (NTP), Occupational Safety and Health Administration (OSHA), and American Conference of Governmental Industrial Hygienists (ACGIH). However, the International Agency for Research on Cancer (IARC) has listed kerosene as a probable human carcinogen. Handling of triglyme and kerosene is simplified by their low vapor pressure, meaning that the chemicals will tend to remain in their liquid form (thereby mitigating inhalation hazards). Sodium borohydride is described as capable of causing severe irritation and burns if eaten or let into contact with skin, however it is also not carcinogenic.

Formulation B

In some embodiments, a liquid fuel comprises a dimethylformamide (DMF) solution including at least 1% metal hydride by weight. In certain embodiments, a liquid fuel comprises, by weight, 1% to 18% metal hydride and 82% to 99% DMF. In further embodiments, a liquid fuel comprises, by weight, 5% to 18% sodium borohydride and 82% to 95% DMF. An exemplary composition comprises, by weight, 12% sodium borohydride and 88% DMF that creates a translucent solution with a slight cloudy appearance.

Themochemistry predicts a theoretical I_(sp) of 309.0 seconds with an optimal O/F ratio of 4.30. The sodium borohydride did not recrystallize when stored at room temperature over a span of six months, but the sodium borohydride did precipitate out when stored below 40° F. Upon reheating and remixing though, the sodium borohydride would redissolve. Experimental results have shown that sodium borohydride will completely dissolve in DMF up to concentrations of approximately 18% by weight sodium borohydride.

Drop testing of the exemplary composition indicates ignition delays of 9.1 ms with 88.5% peroxide and 15.0 ms with 86% peroxide, and open-air testing with an injector assembly resulted in a further decrease in ignition delay down to 7.0 ms with 90.6% peroxide. Drop testing of compositions comprising, by weight, 1%, 12%, and 14.5% sodium borohydride in DMF indicates ignition delays of (no ignition), 15.0 ms, and 19.3 ms, respectively, with 87.4% peroxide. As shown in FIG. 5, pressure trace of the nozzled-chamber test indicates a smooth and steady ignition with no overpressures and exhibits no indication of instabilities. After testing, the hardware was found to have a coating of white agglomerate. The agglomerate is most likely oxide powder residue from combustion. The agglomerate was easily wiped off. The agglomerate is shown on the hardware in FIG. 6.

According to MSDS, DMF is an irritant that can be harmful if inhaled or spilled onto skin. Ingestion may potentially cause liver damage, and chronic exposure may result in mutagenic effects. However, DMF has a low vapor pressure which may reduce the likelihood of inhalation.

Formulation C

In some embodiments, a liquid fuel comprises a dimethyl sulfoxide (DMSO) solution including at least 1% metal hydride by weight. In certain embodiments, a liquid fuel comprises, by weight, 1% to 15% sodium borohydride and 85% to 99% DMSO. In further embodiments, a liquid fuel comprises, by weight, 5% to 15% sodium borohydride and 85% to 95% DMSO. An exemplary composition comprises, by weight, 5.3% sodium borohydride and 94.7% DMSO that creates a transparent solution. According to MSDS, DMSO is an irritant that can be harmful if inhaled or spilled onto skin. Ingesting enough DMSO can be lethal; however there are no recognized carcinogenic components.

Themochemistry predicts a theoretical I_(sp) of 298.7 seconds with an optimal O/F ratio of 3.80. The sodium borohydride did not recrystallize when stored at room temperature over a span of six months, but the sodium borohydride did precipitate out when stored at −22° F. Upon reheating and remixing though, the sodium borohydride would redissolve.

Drop testing of the exemplary composition indicates an ignition delay of 17.0 ms with 86% peroxide, and open-air testing with an injector assembly resulted in a further decrease in ignition delay down to 7.0 ms with 90.6% peroxide. Drop testing of compositions comprising, by weight, 1%, 5%, and 10% sodium borohydride in DMSO with 87.4% peroxide resulted in ignition delays of (no ignition), 96.5 ms, and 14 ms, respectively. The ignition delay result of 96.5 ms for a 5% sodium borohydride liquid fuel is based on the average of two widely separated data points, and may not be accurate.

As shown in FIG. 7, pressure trace of the nozzled-chamber test indicates a slight overpressure at ignition followed by an otherwise smooth build-up to full pressure. There are no indications of instabilities. After testing the hardware was found to have a coating of white agglomerates, likely oxide powder residue, that was easily wiped off and was present in lesser amounts than Formulation B. The residue is shown in FIG. 8.

Formulation D

In some embodiments, a propellant comprises a tetraethyl glycol (also described as tetraglyme) solution including at least 1% metal hydride by weight. In certain embodiments, a liquid fuel comprises, by weight, 1% to 15% sodium borohydride and 85% to 99% tetraglyme. An exemplary composition comprises, by weight, 12.3% sodium borohydride and 87.7% tetraglyme that creates a translucent, mildly cloudy solution. According to MSDS, tetraglyme is an irritant that can affect the skin, eyes, and digestive track. Ingestion in large quantities can be lethal; however the chemical is not listed as a carcinogen.

Themochemistry predicts a theoretical I_(sp) of 312.0 seconds with an optimal O/F ratio of 4.29. The sodium borohydride did not recrystallize when stored at room temperature over a span of one month. No data is currently available for lower temperatures.

Drop testing of a composition comprising, by weight, 10% sodium borohydride and 90% tetraglyme indicates an ignition delay of 12.0 ms with 88.5% peroxide. Open-air testing of the exemplary composition above with an injector assembly resulted an ignition delay of 12.0 ms with 90.6% peroxide. As shown in FIG. 9, a pressure trace of the nozzled-chamber test indicates no significant overpressure at ignition and a smooth build-up to full pressure. Pressure oscillations are higher than seen in previous formulations suggesting a possibility of less stable combustion. More testing is required to verify this phenomenon. After testing the hardware was found to have a coating of white agglomerates, most likely oxide powder residue, that was easily wiped off. The residue is shown in FIG. 10.

Additional Components

As an additional component for use in any metal hydride-catalyzed propellant or any exemplary composition such as Formulations A, B, C, or D, it is proposed that a cobalt compound can be further added to the compositions to further catalyze the decomposition of the metal hydride resulting in even lower ignition delays. In several literary sources, compounds such as cobaloximes and cobalt oxides can be used to improve the decomposition of sodium borohydride into hydrogen. The ideal cobalt-based compound would exhibit this catalytic effect and would further also be soluble in the propellant solvents.

Comparison of the Exemplary Compositions

In summary each of Formulations A, B, C, and D described previously have varying characteristics, relative to each other. The following Table 1 is a summary of relevant propellant performance measurement properties for Formulations A, B, C, and D in comparison with triglyme and a current toxic hypergolic propellant combination. Certain properties of Formulations A, B, C, and D are emphasized in bold.

TABLE 1 Summary of Propellant Performance Measurement Properties Drop Test Injector Liquid Fuel/ Relative Ignition Ignition Primary I_(sp) I_(sp) to Delay Delay Solvent [S] MMH/NTO Cost [ms] [ms] MMH/NTO 341.2 n/a High n/a 1 to 3 Triglyme 336.7 98.5 Low/ 10.6 9.0 Moderate Triglyme + 314.0 92.0 Low/ 21.0 n/a Kerosene Moderate DMF 309.0 90.6 Low  9.1 7.0 DMSO 298.7 87.5 Low 14.0 7.0 Tetraglyme 312.0 91.4 Low/ 12.0 12.0  Moderate The I_(sp) in Table 1 is calculated assuming an expansion ratio of 40, a chamber pressure (P_(c)) of 1,000 psi, and use with 90% to 100% peroxide oxidizer. Drop test and injector ignition delay results, apart from MMH/NTO, are from experiments using oxidizers comprising, by weight, about 85% to 91% hydrogen peroxide.

The following Table 2 is a summary of additional properties for Formulations A, B, C, and D in comparison with a current toxic hypergolic propellant combination. Certain properties of Formulations A, B, C, and D are emphasized in bold.

TABLE 2 Summary of Additional Relevant Propellant Properties. Room Low Propellant/ Temper- Temper- Primary ature ature Toxicity/ Solvent Storage Storage Handling Mutagenicty MMH Good Good Requires Both, with moderate special exposure equipment Triglyme + Fair Good Requires Harmful if ingested, Kerosene standard may be lethal if equipment ingested in large quantities DMF Fair Poor Requires Both, with severe standard exposure equipment DMSO Good Poor Requires Harmful if ingested, standard may be lethal if equipment ingested in large quantities Tetraglyme Fair n/a Requires Harmful if ingested, standard may be lethal if equipment ingested in large quantities

While this disclosure has been described as having an exemplary design, the present disclosure may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains. 

1. A propellant comprising: a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising: kerosene, sodium borohydride, and an amount of triethylene glycol dimethyl ether sufficient to dissolve the sodium borohydride.
 2. The propellant of claim 1, wherein the hydrogen peroxide is high test hydrogen peroxide.
 3. The propellant of claim 1, wherein the liquid fuel includes an amount of kerosene within the range of twenty percent (20%) to seventy-five percent (75%) by weight.
 4. The propellant of claim 1, wherein the liquid fuel comprises at least twenty percent (20%) triethylene glycol dimethyl ether by weight.
 5. The propellant of claim 4, wherein the liquid fuel includes an amount of triethylene glycol dimethyl ether within the range of twenty percent (20%) to eighty percent (80%) by weight.
 6. The propellant of claim 1, wherein the metal hydride is sodium borohydride.
 7. The propellant of claim 6, wherein the liquid fuel includes an amount of sodium borohydride within the range of five percent (5%) to fifteen percent (15%) by weight.
 8. The propellant of claim 1, wherein the liquid fuel includes a cobalt compound.
 9. A propellant comprising: a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising: dimethylformamide, and at least one percent (1%) metal hydride by weight.
 10. The propellant of claim 9, wherein the liquid fuel includes an amount of metal hydride within the range of one percent (1%) to eighteen percent (18%) by weight.
 11. The propellant of claim 9, wherein the metal hydride is sodium borohydride.
 12. The propellant of claim 11, wherein the liquid fuel includes an amount of sodium borohydride within the range of five percent (5%) to eighteen percent (18%) by weight, and an amount of dimethylformamide within the range of eighty-two percent (82%) to ninety-five percent (95%) by weight.
 13. The propellant of claim 9, wherein the liquid fuel includes a cobalt compound.
 14. A propellant comprising: a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, and a liquid fuel comprising: dimethyl sulfoxide, and at least one percent (1%) metal hydride by weight.
 15. The propellant of claim 14, wherein the liquid fuel includes an amount of metal hydride within the range of one percent (1%) to fifteen percent (15%) by weight.
 16. The propellant of claim 14, wherein the metal hydride is sodium borohydride.
 17. The propellant of claim 16, wherein the liquid fuel includes an amount of sodium borohydride within the range of five percent (5%) to fifteen percent (15%) by weight, and an amount of dimethyl sulfoxide within the range of eighty-five percent (85%) to ninety-five percent (95%) by weight.
 18. The propellant of claim 16, wherein the liquid fuel is approximately 10% sodium borohydride.
 19. The propellant of claim 14, wherein the liquid fuel includes a cobalt compound.
 20. A propellant comprising: a liquid oxidizer, wherein the liquid oxidizer is at least approximately 70% hydrogen peroxide by weight, a liquid fuel comprising: tetraethyl glycol, and at least one percent (1%) metal hydride by weight.
 21. The propellant of claim 20, wherein the metal hydride is sodium borohydride.
 22. The propellant of claim 21, wherein the liquid fuel includes an amount of sodium borohydride within the range of five percent (5%) to fifteen percent (15%) by weight, and an amount of tetraethyl glycol within the range of eighty-five percent (85%) to ninety-five percent (95%) by weight.
 23. The propellant of claim 20, wherein the liquid fuel includes a cobalt compound. 